1. Field of the Invention
The present invention relates to a method for producing a glass article. In particular, the present invention relates to a method for producing a glass article from glass soot (fine particles) deposit which is produced by a glass soot synthesis method such as a vapor phase axial deposition (VAD) method or a outside vapor deposition (OVD) method.
2. Description of the Related Art
To synthesize a glass soot deposit, there is known a VAD method which comprises jetting a mixture of a fuel gas, a combustion-support gas and a glass-forming raw material from a burner, forming glass soot through hydrolysis or oxidation of the glass-forming raw material in a flame, depositing the glass soot at a tip end of a rotating starting member to form a soot deposit while moving the starting member in relation to the burner as the soot deposit grows. Also, there is known an OVD method which comprises depositing glass soot which is generated with a burner around an peripheral surface of a starting member while traversing either of the burner or the starting member more than one time to form a soot deposit (see, for example, Japanese Patent Kokai Publication No. 73522/1973).
In the synthesis of the glass soot, a multi-flame type burner is proposed to increase deposition efficiency of particulate glass which is generated by the burner on the soot deposit. As disclosed in Japanese Utility Model Publication No. 4979/1985 and Japanese Patent Publication No. 50418/1987, the multi-flame type burner is typically a coaxial multi-port burner which comprises, at a center part, a glass soot-synthesizing port which has a sub-port for jetting the glass-forming raw material, a sub-port for the fuel gas and a sub-port for the combustion-support gas, and at a peripheral part, at least one flame-forming port which protrudes in the direction of the gas stream in relation to an outlet of the glass soot-synthesizing port and has a sub-port for the fuel gas and a sub-port for the combustion-support gas. Hitherto, using such multi-flame type burner, the deposition efficiency of the glass soot has been improved.
The glass-forming raw material is supplied by a bubbling method with a carrier gas as shown in FIG. 3 or a direct supply method using a vapor pressure of the raw material itself, mixed with oxygen gas or hydrogen gas and then introduced in the burner.
In the soot synthesis, development has been directed to increase of a synthesis rate (a weight of a soot preform produced per a unit time) and increase of productivity. However, when a flow rate of the glass-forming raw material is increased to increase the synthesis rate, a ratio of the preform weight to an amount of the synthesized glass which is theoretically calculated from the flow rate of the glass-forming raw material, namely a yield decreases, and therefore, the synthesis rate has an upper limit. To solve such problem, various techniques such as acceleration of gas mixing or control of the gas flow rate (a Raynolds' number) (cf. Japanese Patent Publication No. 28100/1987) have been proposed. However, none of them is an fundamental solution of the problem.
Then, it is highly required to provide a production method of a soot deposit by which the glass-forming raw material is effectively reacted in the flame to grow glass soot and then the grown soot is effectively deposited on a surface of the already deposited soot.